When machining low and medium alloyed steels and stainless steels with cemented carbide tools, the cutting edge is worn according to different wear mechanisms, such as chemical wear, abrasive wear, and adhesive wear and by edge chipping caused by cracks formed along the cutting edge. The domination of any of the wear mechanisms is determined by the application, and is dependent on properties of the machined material, applied cutting parameters, and the properties of the tool material. In general, it is very difficult to improve all tool properties simultaneously, and commercial cemented carbide grades have usually been optimized with respect to one or few of the above mentioned wear types, and have consequently been optimized for specific application areas.
EP 1493845 relates to a coated cemented carbide insert (cutting tool), particularly useful for milling of stainless steels and super alloys but also milling of steels in toughness demanding applications. The cutting tool insert is characterised by a cemented carbide body comprising WC, NbC and TaC, a W-alloyed Co binder phase, and a coating comprising an innermost layer of TiCxNyOz with equiaxed grains, a layer of TiCxNyOz with columnar grains and a layer of α-Al2O3.
WO 97/20083 discloses a coated cutting insert particularly useful for milling of low and medium alloyed steels and stainless steels with raw surfaces such as cast skin, forged skin, hot or cold rolled skin or pre-machined surfaces under unstable conditions. The insert is characterized by a WC—Co cemented carbide with a low content of cubic carbides and a rather low W-alloyed binder phase and a coating including an innermost layer of TiCxNyOz with columnar grains and a top layer of TiN and an inner layer of κ-Al2O3.
WO 97/20081 describes a coated milling insert particularly useful for milling in low and medium alloyed steels with or without raw surface zones during wet or dry conditions. The insert is characterized by a WC—Co cemented carbide with a low content of cubic carbides and a highly W-alloyed binder phase and a coating including an inner layer of TiCxNyOz with columnar grains, an inner layer of κ-Al2O3 and, preferably, a top layer of TiN.
EP 1103635 discloses a cutting tool insert particularly useful for wet and dry milling of low and medium alloyed steels and stainless steels as well as for turning of stainless steels. The invented cutting tool is comprised of a cemented carbide body with a coating consisting of an MTCVD Ti(C,N) layer and a multi-layer coating being composed of κ-Al2O3 and TiN or Ti(C,N) layers.
WO 2007/069973 discloses a coated cutting tool insert particularly useful for dry and wet machining, preferably milling, in low and medium alloyed steels, stainless steels, with or without raw surface zones. The insert is characterized by a WC—TaC—NbC—Co cemented carbide with a W alloyed Co-binder phase and a coating including an innermost layer of TiCxNyOz with columnar grains and a top layer at least on the rake face of a smooth α-Al2O3.
What is needed is a coated cutting tool with enhanced performance for milling of steel. The invention is directed to these, as well as other, important needs.